The present application relates generally to conductive interconnect structures, and more specifically to cobalt-based interconnect structures and barrier layer architectures that improve the mechanical integrity of such structures.
Electrically-conductive connections between integrated circuit (IC) devices formed on a semiconductor substrate are traditionally made using multi-layer interconnects. Each interconnect layer can be supported over the substrate by an interlayer dielectric. Furthermore, electrical connections to and between different conductive layers are commonly made using contacts in the form of plugs that traverse one or more layers of the interlayer dielectric.
Typical interconnect structures comprise copper (Cu) or tungsten (W). Copper is advantageous because of its low electrical resistivity. However, copper is susceptible to electromigration and void formation, which can lead to device failure, while the precursors used during tungsten CVD processes are highly reactive with silicon and associated liner materials. Thus, tungsten is particularly sensitive to defects (e.g., pin-hole defects) in the barrier layer architecture used to isolate the tungsten interconnects from the liner metal and silicon.
In addition, tungsten resistivity cannot be decreased with post-deposition annealing as it is a refractory metal and does not undergo recrystallization or grain growth at thermal budgets that are compatible with semiconductor manufacturing. Moreover, it has been observed that the barrier and nucleation layer thicknesses for tungsten-based metallization are not scaling to meet resistance requirements at advanced nodes.
An alternative interconnect material to copper and tungsten is cobalt. Due to a higher activation energy, cobalt is less prone to electromigration compared to copper, and is compatible with thin barrier layer architectures, which can be especially advantageous at advanced nodes, e.g., less than 14 nm. Processing subsequent to the formation of cobalt contacts, however, including annealing to induce reflow and recrystallization, can introduce stresses that compromise the mechanical integrity of cobalt contacts, including failed adhesion to underlying barrier layers. Delamination and void formation can undesirably increase contact resistance or cause device failure.